1. Field of the Invention
This invention relates to an electromagnetic actuator, an optical scanner using an electromagnetic actuator and a method of preparing an electromagnetic actuator.
2. Related Background Art
Conventional actuators prepared by utilizing the micro-machining technology are mostly based on the use of electrostatic force or piezoelectric phenomena. However, thanks to the availability of the micro-machining technology for utilizing magnetic materials in recent years, actuators using electromagnetic force have been developed.
FIG. 1 of the accompanying drawings schematically illustrates a linear actuator that utilizes an electromagnetic force for positioning the head of a hard disk as disclosed in U.S. Pat. No. 5,724,015. Referring to FIG. 1, the actuator comprises a pair of cores 1004a, 1004b rigidly secured to a substrate (not shown) and a pair of coils 1005a, 1005b wound around the respective cores along with a movable member 1003 so supported by springs 1007 as to be movable relative to the cores 1004a, 1004b. The above-described structure is formed on the substrate by means of micromachining technology.
As electric power is supplied to the coil 1005a of the actuator, the movable member 1003 is pulled toward the core 1004a to consequently displace the movable member 1003 to the left in FIG. 1. When, on the other hand, the coil 1005b is electrically energized, the movable member 1003 is displaced to the right in FIG. 1. The force F1 generated in the actuator is expressed by formula (1) below;F1=0.5μ0N12i12w1t1(d1−x1)−2   (1 )where μ0 is the magnetic permeability of vacuum, N1 is the number of turns of the coils, i1 is the electric current made to flow to the coil 1005a or 1005b, w1 is the width of the magnetic pole, t1 is the thickness of the magnetic pole and d1 is the length of the gap. If the spring constant of the springs 1007 is k1, the displacement x1of the actuator is expressed by using the relationship of formula (2) below;F1=k1x1  (2)
However, since actuators having a configuration as described above by referring to FIG. 1 show a large leakage of magnetic flux, they are accompanied by the problem of a poor energy efficiency. Additionally, since the number of turns of the coils of such an actuator is limited due to the structure where only the stationary members are provided with coils, the actuator is also accompanied by the problem of a weak generated force.